» Microcra PHA. 
Dés Cartes principles,by conceiving thé Globulsof’ the thirdiElemeht td 
find lefs-and lefs refiftance againtt that fide of themwhich: ; 
or by a way, which Ehave further-explicated in debcuitantho ne 
Jowrs, robe from an obliquatiomof the pulfe of light, whenee the alder 
part!is continually promoted, and prices ‘refracted, towards the 
pexpendicular, which cuts the Orbs at rightanglés. -, What! the pariticus 
_lanFigure of the Curve line, defcrib'd by this way of light, is, I thall ns 
now tand to examine, efpecially fince there may be fo many-forts of it ds 
there tay be varieties of the Pofitions of the inter'mediat degrees of ders 
fityxbd ‘rarity between the bottom and: the top: of :the infledting Mediuri 
I could produce many more Examples be: riments, :t0 ilinftrate 
and prove this firft Propofition, vz. that theres uch: a.conftitution of 
fome bedies as will caufe intlection. As not to mention thofe I have ob- 
.. Fake a {mall Gla&-bubble; made in the form of that in the fecond 
Figure of the 37. Scheme, and by heating the Glafs very hot, and there- | 
by a rarifying the included Air, or, which is better, by ravify+ | 
ing a {mall quantity of water, included in it, into vapours, .which. will | 
expel the moft part, if not all the Air, afd thenfealing up the {mall 
neck of it, and letting it cool, you may find, if :you placeit in a conve- 
ae Inftrument, that there will be.a manifeft difference, as tothe refta- 
ons : : oe Al pant Ss 4 
_. As if in this fecond Figure you fuppofe A to reprefent a {mall fight 0 
hole, through which the eye looks upon an objedt, as C, through” 
Glafs-bubble B, and the fecond fight L5 all which rethain'exactly fixt 
in their feveral places, the object C being fo cized and placed, that i¢ 
may juft feem to touch the upper.and under edge of the hole L: and 
fo.allof it be teen through the fmall-Glafs-ball of rarified Air 5 then by 
breaking 
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